The most recent list of best-converting sites is just published on my blog.
I split the "Traffic Source" column into 2 separate columns. They are the "Traffic Site" and the "Source".
The "Traffic Site" column shows you the actual site that generated traffic and signups.
The "Source" column shows you the way I used to reach the site audience. It can be "Banner", "Mailer", "Solo", "Link in the Email Body", "Login Ads", etc.
Read that list and see if you are missing out on any of these traffic sources. Spend your time only on sites that are proven to convert.